I have a shed overgrown with climbing plants outside and inside, so i never go in it, (spiders etc). The concrete base that it stands on looks quite pebbly not smooth like normal concrete, and I have noticed this year that all along this base holes are appearing a bit like mouse holes. I pushed a large pebble in one of these holes and it looks as if it has been pushed aside. Is this likely to be some sort of animal or a crumbling of the base itself, it is quite a worry. Janet PS this shed was in the garden when we bought the bungalow and has not been entered for at least 10 years!!
You sure it's concrete?! Sounds like could be a compacted dry/weak mix or compacted MOT or Ballast. Sheds don't need much to keep them up tho. You could restore the base in a few mixes by replacing a side at a time, a few inches deep with a new mix of ballast (from a bag) and a bit of cement. 5 or 6 to 1 (ballast to cement) is ample for that job.
Is there any reason why you can't get the shed demolished and taken away? The base may be asbestos. You don't say where you live but it sounds as if mice/rats may have taken up residence. (Can't blame them if you don't use it, lol.)
Ha ha actually mad maggot you have said what I was afraid of. . The trouble is there is a beautiful clematis which has obviously been there for years its stems are almost like tree trunks, and its lovely. The shed itself also looks in good condition, but I think proabably you are right. Who would I go to if I decide to have it demolished - a gardener, a builder or a rat catcher!!!!!!!!!!!!!! Janet